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JavaScript JavaScript Loops, Arrays and Objects Tracking Data Using Objects Using `for in` to Loop Through an Object's Properties

Posted by ammarkhan
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ammarkhan
Front End Web Development Techdegree Student 21,661 Points

How key becomes a value

While studying objects, we use 

for (var key in value){
      console.log(key)
    }

to access key of the object, but when we want to access its value we use

    for (var key in value){
      console.log(value[key])
    }

I find it confusing that while we wanted to find out about only the keys, we used the first part key but when we wanted to find out its value, the same key is passed as a value.

Brian Ball
Brian Ball
23,661 Points
Brian Ball
Brian Ball
23,661 Points

you'll need to translate code to words you understand. this could be more clear if written like:

for (var item in listOfItems) { console.log(listOfItems[item]) }

I translate this code as saying: for each key in the object(array) stored in a variable called value, console log the value of the item retrieved from the object named value referenced by value[key] <-- here, we're retrieving the value with the key (see how to reference an item in an object)

Imagine it looks like this value = { "key0" : value0, "key1" : value1 }

because you're using a for loop, the 0 and 1 are invisible as the loop is traversing each item

1 Answer

Steven Parker
Steven Parker
231,236 Points
Steven Parker
Steven Parker
231,236 Points

It's not entirely correct to say "the same key is passed as a value." It would be more accurate to say "the same key is used as an index to access the value".

Another factor that might be making this particular example more confusing is the use of the word "value" to represent the object. So an example like this might make it more clear:

for (var key in object) {
    var value = object[key];
    console.log(`object.${key} = '${value}'`);
}